FT-ICR Detection System for KATRIN

Motivation and Experimental Set-up

The FT-ICR Penning Trap Detection System (a prototype of a cylindrical three-electrode
Penning Trap) in Heidelberg is being developed for KATRIN
[1-3]. The KATRIN experiment has been designed to measure the mass of the electron
antineutrino directly with a sensitivity of 0.2 eV, one order of magnitude better than the
present upper limit. The intended sensitivity will be obtained by analyzing the end-point
of the β spectrum from the decay of tritium gas
molecules T2 → (3HeT)+ + e- + νe
.

The KATRIN set up [1-4] comprises a gaseous tritium source, a transport section
pre-spectrometer, the main spectrometer and the detector. In the main spectrometer the electrons from the decay
are guided by a strong magnetic field and analyzed using electrostatic fields. The
tritium gas is removed from the system by differential pumping and cryogenic trapping.
The formation of ion clusters (T2n+1)+ which decay with different end-points
than T2, will prevent unambiguous analysis of the end-point of the tritium decay.
Therefore, the knowledge of the concentrations of these ions is essential to evaluate
the β spectrum.

Figure 1: FT-ICR detection system at the MPIK in Heidelberg
- click for bigger version

The best way for a precise determination of these concentrations is the use of
Penning traps with FT-ICR detection systems. Actual photos of the set up in
MPIK-Heidelberg and the FT-ICR Penning Trap are shown in Figure 1 and 2, respectively.
More details can be found in Ref. [4]. These Penning Trap systems will be located in
the transport section (see also Fig. 1 of Ref. [4]).

Recent Results

There are three main results so far [4]. One of them is that the amplitude of the
FT-ICR signal was recorded for corresponding νexc frequency for different species.
The amplitude of the FT-ICR signal versus excitation frequencies are shown for the
He+, H2O+ ions in Fig. 3. The other result is that
the FT-ICR signal at νrf = ν+ was
recorded for different potentials applied to the end-cap electrodes. Applying
a linear fit to the data (see Fig. 5 of Ref.[4] and using the mass value of the
interested ion, the magnetic field was obtained. This measurement was done for
the He+ and H2O+ ions. The last recent result is that the Penning Trap was
dedicated to determine the minimum number of the ions needed to observe an
FT-ICR signal at room temperature. For further details, see Ref. [4]. All the
measurements were performed at room temperature and all the species
(He+, N2+, and H2O+) were identified by exciting the ion motion at their
modified cyclotron frequency.